The invention relates to an arrangement of sheet-holding systems at storage drums in turning devices of sheet-fed printing machines.
Turning devices, which operate according to the three-drum turning principle, consist of three sheet-guiding cylinders, the diameter of the center one of which is twice as large.
Such a turning device enables sheets to be turned according to the rear edge principle of turning sheets and, with that, the sheets to be printed either recto or recto and verso in one pass.
The storage drum has two sheet-holding systems for the front region and two sheet-holding systems for the rear region of the sheet, which are diametrically opposite to one another. The sheet-holding systems can be adjusted relative to one another in the circumferential direction, so that sheets of different length can be processed.
From the publication DE 39 11 630 C2, an arrangement of sheet-holding systems at a storage drum is known. The sheet-holding system for the front region of the sheet, which is constructed as a clamping gripper, is disposed permanently at the body of the storage drum. The sheet holding system, which is constructed as a suction system, is provided at a supporting element, which is detachably disposed at the body of the storage drum.
The supporting element and, with that, the suction device provided at the supporting element, can be adjusted in the circumferential direction by means of an adjusting shaft, which is mounted in the drum leg. A motor for actuating the adjusting shaft is disposed over a gear wheel step at one end of the adjusting shaft (on the outside) and a pinion is disposed at the other. The pinion engages a toothed segment, which is connected with the supporting element. The adjusting shaft is mounted eccentrically in the drum shaft.
If it is necessary to adjust the sheet-holding systems relative to one another in the circumferential direction of the storage drum, the adjusting shaft, which acts over the pinion and the toothed segment on the supporting element, is rotated by means of the motor and the gear wheel step. The suction device is shifted with the supporting element relative to the clamping gripper.
The large expenditure for parts is a disadvantage of such an adjusting device of the sheet-holding systems. Many gearing elements engage one another with clearance, so that the adjustment of the sheet-holding systems with respect to the dimensions of the sheet, which is to the processed, is inaccurate. The drilling and milling in the drum shaft lead to a weakness in the drum leg.
The DE 39 008 18 C1 shows a sheet-guiding drum with an inner shaft and an outer drum with at least one segment, which can be adjusted in the circumferential direction with respect to the inner shaft. The sheet-holding systems are assigned to the inner shaft and the outer drum, which are coupled together by means of a multiple-plate clutch.
The clutch is between an end surface of the segments and a journal pin of the shaft. The clutch can be actuated over a tie rod, which can be actuated from the outside, and a clamping lever and, with that, the connection between the shaft and the segment can be undone. After that, both can be adjusted relative to one another with the sheet-holding systems.
The large expenditure for parts is a disadvantage of this fixing and loosening device. Access to the clutch within the bearing of the sheet-guiding cylinder for maintenance work in the event of wear and contamination is difficult. In this case also, the drilling and milling leads to a weakness in the leg.
It is an object of the invention to provide an arrangement of sheet-holding systems at storage drums, which ensures a stiff construction of the storage drum and a simple adjustment of the sheet-holding systems relative to one another.
Pursuant to the invention, this objective is accomplished by the distinguishing features as claimed.
Due to the arrangement of a central axis in the basic body of the storage drum, which is connected with the suction system by means of the side disks and over the cam and the cam bolt, the stiffness of the basic body of the storage drum is not reduced, since the elongated holes are disposed on the operator side of the printing machine in the storage drum, while the adjustability of the sheet-holding systems by simple means is ensured.
This mounting and arrangement of gripper system and suction system at the storage drum enables the clutch for the systems to be disposed outside of the storage drum. With that, as a result of the good accessibility, the clutch can be manipulated easily.